Chapter 10

Fundamentals of Electricity

Introduction

• This chapter covers the following topics:• Matter, elements, and compounds• A closer look at atoms• Current• Voltage• Resistance

Matter, Elements, and Compounds

• Everything can be broken down into elements or compounds

• Matter– Anything that occupies space and has weight

• Element– Basic building block of nature

Matter, Elements, and Compounds (cont’d.)

• Molecule– Smallest part of a compound that still retains

properties of the compound• Atom

– Smallest part of an element that still retains properties of the element

Matter, Elements, and Compounds (cont’d.)

• Compounds– Chemical combination of two or more

elements• Mixtures

– Physical combinations of elements and compounds

– Examples: air, salt water

Matter, Elements, and Compounds (cont’d.)

• Atom made of protons, neutrons, and electrons– Protons and neutrons form nucleus– Electrons orbit the nucleus

• Electrons orbit in shells– Shells at various distances from the nucleus

Matter, Elements, and Compounds (cont’d.)

• Current– Movement of free electrons– Electrons become free when released from

outermost shell• Voltage

– External force needed to create current

Matter, Elements, and Compounds (cont’d.)

• Resistance– Opposition to the flow of current

Figure 10-1 A compound is the chemical combination of two or more elements. A molecule is the chemical combination of two or more atoms. This example is water (H2O) and salt (NaCl). © 2014 Cengage Learning.

A Closer Look at Atoms

• Atoms of different elements differ from each other

• Protons are positively charged• Neutrons have no charge• Electrons are negatively charged• Atomic number

– Number of protons in atom’s nucleus

A Closer Look at Atoms (cont’d.)

• Atomic weight :• Mass of the atom• Determined by number of protons and

neutrons in the atom’s nucleus• Mass of an electron is insignificantly small

Figure 10-2 Parts of an atom. © 2014 Cengage Learning.

Figure 10-3 The electrons are held in shells around the nucleus.© 2014 Cengage Learning.

Figure 10-4 The number of electrons each shell can accommodate.© 2014 Cengage Learning.

A Closer Look at Atoms (cont’d.)

• Valence shell– Outer shell– Number of electrons in the valence shell is

called the valence• The farther the valence shell is located

from the nucleus:– The less attraction the nucleus has on each

valence electron

A Closer Look at Atoms (cont’d.)

• Conductivity of an atom depends on its valence band– The greater number of electrons in valence

shell, the less it conducts• Valence shell electrons can gain energy

– With sufficient energy, they can leave the atom and become free electrons

A Closer Look at Atoms (cont’d.)

• Conductors– Materials containing a large number of free

electrons• Insulators

– Absorb valence electrons from other atoms to fill their valence shells• Eliminates free electrons

Figure 10-5 Conductivity of various metals.© 2014 Cengage Learning.

Figure 10-6 Copper has a valence of 1.© 2014 Cengage Learning.

A Closer Look at Atoms (cont’d.)

• Semiconductors– Neither good conductors nor insulators– Can be altered to function as conductor or

insulator– Examples of semiconductor materials: silicon

and germanium• Ionization

– Process of gaining or losing electrons

Current

• Signified by symbol I• Sum of charges of moving electrons past a

given point• One coulomb

– The charge of 6.24 x 1018 electrons added together

Current (cont’d.)

• One ampere– One coulomb of charge moving past a single

point in one second

Voltage

• Current flows between two ends of a conductor:– When one end is positively charged and the

other negatively charged• Potential

– Source that creates the charge difference

Voltage (cont’d.)

• Voltage :• Force that moves electrons in a circuit• Also called electromotive force (emf)• Represented by symbol E• Unit is the volt (V)

Figure 10-8 Electrons flow in a circuit due to difference in potential© 2014 Cengage Learning.

Resistance

• Opposition to the flow of electrons– Caused by atoms that do not readily give up

electrons• Every material offers some resistance

– Conductors have low resistance– Insulators have high resistance

• Resistance is measured in ohms (Ω)